Method and apparatus for filtering gas with a moving granular filter bed

ABSTRACT

A method and apparatus for filtering gas ( 58 ) with a moving granular filter bed ( 48 ) involves moving a mass of particulate filter material ( 48 ) downwardly through a filter compartment ( 35 ); tangentially introducing gas into the compartment ( 54 ) to move in a cyclonic path downwardly around the moving filter material ( 48 ); diverting the cyclonic path ( 58 ) to a vertical path ( 62 ) to cause the gas to directly interface with the particulate filter material ( 48 ); thence causing the gas to move upwardly through the filter material ( 48 ) through a screened partition ( 24, 32 ) into a static upper compartment ( 22 ) of a filter compartment for exodus ( 56 ) of the gas which has passed through the particulate filter material ( 48 ).

CROSS REFERENCE TO A RELATED APPLICATION

This application is based upon Provisional Patent Application Ser. No.60/314,103 filed Aug. 22, 2001 and Provisional Patent Application Ser.No. 60/388,201 filed Jun. 12, 2002.

GRANT REFERENCE

Work for this invention was funded in part by a grant from the UnitedStates Department of Energy, Contract No. DE-FG26-99FT40588. Thegovernment may have certain rights in this invention.

BACKGROUND OF THE INVENTION

Counterflow of gas and particles is highly desirable in moving bedgranular filters to achieve high dust removal efficiency fromcontaminated gas streams. In counterflows the dirty entering gas isscrubbed by the dirtiest particles and the clean exiting gas is scrubbedby the cleanest particles. However, moving bed granular filters thatutilize counterflow typically have a low gas throughput to prevent bedmaterial from leaving the filter when the minimum fluidization velocityof the granules is exceeded.

A disadvantage of the cyclonic flow of the gas is a disturbance ofgranules and collected dust at the interface between the gas andgranular bed. Momentum transfer from the cyclonic gas flow imparts aswirling flow to the granules and collected dust, which makes the flowthrough the filter non-uniform and adversely imparts filtrationefficiency.

The lack of durable, low-cost filters to clean high temperature gasstreams is one of the primary obstacles to commercial introduction ofadvanced power systems based on coal and biomass. The two most promisingfiltration systems being investigated by government and industry areceramic barrier filters and moving bed granular filters.

Ceramic barrier filters have several disadvantages: they must beperiodically regenerated (blow back) to remove accumulated dust; theyare fragile; and they are expensive.

Moving bed granular filters have been developed in several differentgeometries. These can be roughly characterized as parallel flow,counterflow, and crossflow filters. Parallel flow of gas and particlesresults in clean gas disengaging from dust-laden granules. Under thesecircumstances, dust can be entrained with the gas, which reduces thedust collection efficiency of the filter. Crossflow filters require verycomplicated tuyeres to inject dirty gas into the moving bed of granules.These are expensive and do not fully solve the dust carryover problem ofgas disengagement.

Moving bed granular filters operate on the principle that a flowing bedof particles can effectively scrub particulate contaminant from a gasstream. Although very promising for achieving high filtrationefficiencies, the relatively large footprint of the equipment and highthroughputs of granular material as filter media are cited as drawbacksto moving bed granular filters.

It is therefore a principal object of this invention to incorporatethese novel design features: A tangential gas inlet, a flowstraightening section at the interface between entering gas and thegranular bed, a screened gas disengagement section, and a diamond shapedinsert.

These and other objects will be apparent to those skilled in the art.

SUMMARY OF THE INVENTION

The design of this invention consists of four main features: atangential gas inlet, a flow straightening section; a gas disengagementsection as shown in FIG. 1, and a diamond shaped insert to enhancefilter material flow. The gas enters the filter through a tangential gasinlet, which imparts a cyclonic motion to the gas flow.

The filter of this invention employs a counterflow of gas and particles,which substantially eliminates the problem of dust carryover in the gasdisengagement region. Upward flowing gas can fluidize the granular bedat sufficiently high flow velocities, which greatly reduces filterefficiency and must be avoided. In the instant design, this problem iseliminated by use of a screen at the disengagement interface between theexiting gas and the granular bed. The screen prevents the bed fromexpanding; thus, it is not able to fluidize. With the screen in place,the gas flow rate through the filter is increased by as much as 67%,which translates to smaller, more economical filters.

Another advantage of the filter of this invention compared to othermoving bed filter designs is the use of a tangential gas inlet, whichreduces pressure drop through the filter. Traditional gas inlets injectgas perpendicularly through the side of the filter housing, whichresults in a large irreversible loss of gas momentum. The tangentialinlet converts linear momentum of the gas flow into a cyclonic flow. Thepreserved momentum of the gas reduces pressure drop by 28-45% comparedto a conventional perpendicular gas inlet.

In an alternate design, a diamond-shaped insert is in the lower regionof the housing to change the media flow pattern, which enhances theperformance of the filter.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic vertical sectional view through the filter systemof this invention;

FIG. 2 is an enlarged scale sectional view taken on line 2-2 of FIG. 1;

FIG. 3 is an enlarged scale sectional view taken on line 3-3 of FIG. 1;and

FIG. 4 is a view similar to that of FIG. 1, but shows an alternateembodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to FIG. 1 the filter assembly 10 has a conventionalsupporting frame 12 which supports a filter compartment 14 which iscylindrical in shape. The filter compartment has a top 16 with a centeropening 17, a bottom 18, and cylindrical side walls 20. An uppercompartment 22 serves as a gas disengagement region and has a bottompartition 24 with a center opening 26 directly below center opening 17in top 16. A vertically disposed hollow particle inlet conduit 28extends downwardly through the center opening 17 of top 16 as well asthrough the opening 26 in bottom partition 24 (FIG. 2). The opening 26in bottom partition 24 is sufficiently large to provide a circular space30 around inlet conduit 28 (FIG. 2). A screen mesh 32 extends over space30 and is connected to bottom partition 24 in any convenient manner.

A plurality of radially disposed horizontal fins 34 are located in thegas engagement section 35 of filter compartment 14 at a level below thelower end of the inlet conduit 28. The bottom 18 of filter compartment14 has tapered bottom conical side walls 36 which terminate at the lowerend thereof in exit port 38. Port 38 is sealed to auger boot 40. Asealed auger assembly 42 is conventionally connected to auger boot 40 ina sealed manner, and conventionally extends upwardly and outwardlytherefrom. The upper end of the auger assembly 40 is in sealingengagement with a conventional residue container 44 by means of a sealedbut detachable connection 46.

In FIG. 1, a filter material 48 is placed in supply bin 49 which is inconnection with the upper end of inlet conduit 28. The numeral 48A(FIG. 1) designates an inverted conically-shaped pile or mass of thefilter material which has entered the gas engagement section 35 throughthe inlet conduit 28. While the shape and size of the mass 48A may varyin size and shape during the operation of the filter assembly 10, itwill always be sufficiently broad at its upper end to cover the completearea of the screen mesh 32. It typically will extend downwardly belowthe radial fins 34 to create a gas engagement section 50 where the gasinterfaces with the surface of the filter material 48. It should also benoted that a sufficient quantity of the filter material 48 completelyfills the bottom of a filter compartment 14. The material in exit port38, boot 40, and in auger assembly 42 effectively seals the bottom ofthe filter compartment to prevent the escape of any gas material throughthose components. A valve 52 in the bottom of the filter compartment isavailable for selective access into the filter compartment from thebottom as maintenance or the like may require.

A horizontally disposed gas inlet 54 is tangentially secured to thefilter compartment 14 at a level below the bottom partition 24 of theupper compartment 22. A horizontal gas inlet pipe 56 extends outwardlyfrom upper compartment 22 and serves to exit filtered gas from the uppercompartment 22 as will be described hereafter.

It should be understood that the filter material 48, which is granularin nature and which will be described hereafter is continuously flowingdownwardly through the filter compartment 14. The material is not freefalling through the filter, for its downward movement is controlled andis restricted by the auger assembly 42 which determines and regulatesthe discharge of the filter material from the filter compartment 14.

In operation, gas under pressure is introduced into the gas engagementsection 35 through inlet 54 after the filter material 48 hassufficiently filled the filter compartment 14 to the extend completelyunder screen 32 as shown in FIG. 1. Again, it is important to note thatthe filter material at that point in time covers the lower surface ofscreen 32 to prevent any gas material from flowing from the inlet 54directly into the upper compartment 22 through the screen 32. The arrows58 designate the general cyclonic path of the injected gas from inlet 54around the surface of the conical shaped pile 48. This cyclonic path iscreated by virtue of the tangential location and direction of the gasinlet 54. As the gas approaches the fins 34, the cyclonic path of thegas is interrupted and is changed to a vertical direction as indicatedby the arrows 60. It is within the engagement section 50 that the gasinterfaces with the filter material 48 and begins to migrate upwardlythrough the conical shaped pile or mass of filter material 48A asindicated by the arrows 62. The upwardly moving gas through the material48A will not penetrate the inlet conduit 28 because of the weight anddownward movement of the filter material moving downwardly therethrough.Rather, the gas will proceed to the area of least resistance whichcauses it to move upwardly through the screen 32 into the uppercompartment 22. The gas is cleansed by the filter material as it movesupwardly against the downwardly flow of the filter material. Thus, thegas entering the upper compartment 22 and exiting through the conduit 56is substantially cleaner than the gas that was entering the gas inlet54.

The three main features of the preferred embodiment of this invention,i.e., a tangential gas inlet, a flow straightening section, and a gasdisengagement section are shown in FIG. 1.

Inside the filter compartment 14, the gas flows swirls downward towardsthe interface between the gas and granular bed (see arrows 58 in FIG.1). By imparting cyclonic flow, the momentum of the gas is preserved,reducing pressure drop normally associated with sudden expansion into afilter. However, bed granules and accumulated dust cake on the surfaceof the bed would be disturbed unless the radial component of the gasflow is redirected axially before it reaches the bed surface. The gas isredirected by a flow straightening fins 34 above surface of the bed,which consists of sixteen evenly spaced fins distributedcircumferentially in the annular space. The fins 34 effectively redirectthe radial momentum of the flow axially downward (arrow 60) onto thegas-solid contacting or engagement region 50. The flow-straighteningregion 50 effectively distributes the gas flow over the surface of thebed, which is important to the efficient utilization of the filtermedia. It is at this gas/solid interface that much of the gas cleaningtakes place: dust particles entrained in the gas flow impact ongranules, where they are effectively captured. The accumulation of dustparticles on the granules and in the voids between granules forms a thindust cake, which further aids in the capture of dust particles in thegas flow.

The gas flows upward (arrows 62) through the granular material, which ismoving downward as a moving bed. This counterflow of gas and granulesmeans that the dirty gas engages the bed where the granules are thedirtiest while clean gas disengages the bed where the granules are thecleanest. This counterflow results in very efficient gas cleaning.

The gas disengagement region (upper compartment 22) consists of acentral pipe 28 that feeds granular material to the top of the movingbed and an annular region 35 where clean gas exits the bed through ascreen. As previously indicated, gas does not flow into the inletconduit 28 by virtue of the large gas flow resistance in that direction.Gas flowing upward in the upper compartment 22 around the feed pipetends to expand the bed against the screen, which prevents the movingbed from transitioning to a fluidized bed even at very high gas flowrates. This constraint is important because a fluidized bed would not beas efficient as a moving bed for dust collection.

As gas flows through the filter, the granular bed is continuouslyflowing downward under the force of gravity. The granular bed flow rateis controlled using either the slide gate (valve 52) positioned at thebottom of the unit, or the auger boot 40 and auger assembly 42 asdescribed above.

Certain tests were conducted to determine the feasibility of theinvention. For the tests described here, all parts were constructed from¼″ thickness polycarbonate plexiglass to give a clear view of bed fluiddynamics. The part dimensions and shapes are listed in Table 1 below:

TABLE 1 Size and Shape of Design Parts Part Size and Shape Gas Inlet 54 4″ × 4″ OD tube Filter Compartment 14 12″ × 4″ OD tube UpperCompartment 22  8″ × 4″ OD tube Fins 34  ¾″ × 3″ rectangle Inlet Conduit28  4″ × 4″ OD tube Gas Exit 56  4″ × 4″ OD tube

Sixteen fins were evenly spaced around the gas disengagement section.The granular bed consisted of washed 4-mm diameter soda-lime glass beadsassumed to be perfectly spherical. Household window screen was stretchedbetween the inlet conduit 28 and gas disengagement section (uppercompartment 22) to prevent fluidization of the granular bed. Air at 70°F. simulated the gas to be cleaned in the model filter. All parts werewelded together using standard plexiglass solvent.

Other parts used in these tests include a sealed funnel, slide gate, anda 5-gallon container. The granular bed material was stored above thefilter compartment in the funnel where it flowed downwardly into thegranular inlet conduit by gravity. It then flowed into the gasdisengagement section and through the slide gate valve into the 5-galloncontainer.

The main purpose of the above tests was to establish gas and granularflow characteristics of the filter assembly. In addition to visualobservations of the granular flow, pressure drop in the gas flow betweenthe gas inlet and gas exit was measured as a function of incrementedsuperficial gas velocities. For the purposes of these tests, superficialvelocity was defined as the volumetric flow rate divided by the crosssectional area of the annular interfacial area where inlet gas engagesthe moving bed. Bed depth, cross-sectional flow area, granular size anddensity, and gas travel distance were kept constant in these tests.

The pressure drop was recorded at each superficial gas velocity usingthree Magnahelix differential pressure gauges (2, 5, and 10 in. H₂O).Three differential pressure gauges were used to increase recordingaccuracy at different gas flow rates. A vertical, in-line 0-606 ft/min(0-100 SCFM) rotameter, corrected for temperature and pressure, was usedto measure volumetric flow rate of air. Prior to each test, thedifferential pressure gauges and rotameter were calibrated at zero toensure accurate measurements.

Triplicate measurements were performed for superficial gas velocitiesbetween 0 to 606 ft/min in increments of 30 ft/min. At each gas flowrate, the granular bed material was allowed to flow for five minutes toreach steady state before the gas flow rate, differential pressure, andvisual observations of moving bed behavior were recorded.

It was hypothesized that the formation of dust cake to be important forefficient dust collection, the entering gas flow must not disrupt theinterfacial area between bed and gas. This was accomplished by lettinggranules flow out of a solids downcomer (inlet conduit) to spread outinto a large, conical interface. Dirty gas flows downward through thisinterface, depositing dust, and then turns to flow upward through thedownward flowing granular bed.

The gas disengagement region (upper compartment) also required a specialconfiguration to allow high gas flows through the filter. The upwardflowing gas induced a drag on the granules that causes the bed to expandand eventually fluidize, an undesirable behavior that limits gasthroughput through the filter. A gas disengagement section (uppercompartment) consisting of a small diameter feeder tube conveyinggranular material to a larger diameter was used. At low gas velocities,the granules from the feeder tube spread out into a conical pile.However, at high gas velocities, these particles expanded upward againstan annular porous plate or screen that prevented their continuedexpansion. The screen allowed gas to exit the filter while retaininggranular material. Gas did not enter the feeder tube by virtue of thelarge gas flow resistance in that direction.

The filter was constructed from 6.35 mm thick polycarbonate plexiglassto give a clear view of bed fluid dynamics. The body of the filter was19.8 cm dia., the downcomer (inlet conduit) was 14.2 cm dia., and thefeeder tube was 10.2 cm dia. The feed hopper (49) provided freshgranular material to the top of the filter. A discharge barrel, whichwas sealed against the atmosphere, accepted dust-laden granular materialfrom the bottom of the filter. Air at 20° C. simulated the gas to becleaned in the filter. The granular bed is comprised of washed 4-mmdiameter soda-lime glass beads assumed to be perfectly spherical. Thegranular bed flow rate was controlled with a slide gate at the bottom ofthe filter. Bed depth, cross-sectional flow area, granular size anddensity, and gas travel distance were kept constant in these tests.

As previously indicated, a rotameter, corrected for temperature andpressure, was used to measure volumetric flow rate of air up to 2.8m3/min. Pressure drop was recorded at each superficial gas velocityusing three Magnahelic differential pressure gauges (5, 12.7, and 25.4mm H₂O). Three differential pressure gauges were used to increaserecording accuracy at different gas flow rates. Triplicate measurementswere performed for superficial gas velocities between 0-3.1 mls inincrements of 0.15 m/s. At each gas flow rate, the granular bed materialwas allowed to flow for five minutes to reach steady state before thegas flow rate, differential pressure, and visual observations of themoving bed were recorded. In some experiments, titanium oxide smoke wasinjected into the air flow to visualize gas entering the filter andobtain a qualitative indication of filtration efficiency.

Qualitative observations were made on the behavior of granular materialmoving through the downcomer as a function of superficial gas velocity,which is defined as the volumetric flow rate divided by the crosssectional area of the annular region formed between the filter body andthe inlet conduit. The filter was tested both with and without theretaining screen installed above the disengagement section. Observationson the behavior of the granular bed in the presence and absence of thescreen are recorded in Tables A and B. Without the screen, granules atthe surface of the bed in the disengagement section become agitated withincreasing superficial velocity and eventually elutriate from thefilter. It was estimated that the maximum operating velocity to be 0.9mls without a retaining screen. When the screen was installed above thedisengagement section, the granules expand against the screen but werenot able to fluidize. It was estimated that the maximum operatingvelocity to be 1.5 m/s. The screen increased gas throughput by 67%compared to the filter operated without the screen.

TABLE A Performance of downcomer with retaining screen in disengagementsection Superficial gas velocity (m/s) Observations of downcomer flow 0-0.3 Smooth downward granular bed flow with no fluidization. 0.3-0.6Smooth downward granular bed flow. Bed material begins to expand upward.0.6-0.9 Smooth downward granular bed flow. Full expansion of the bedwith the upper region becoming fully fluidized. >0.9 Material in tophalf of downcomer fully fluidized; granular material entrainedelutriated through the gas exit.

TABLE B Performance of downcomer without retaining screen indisengagement section Superficial gas velocity (m/s) Observations ofdowncomer flow  0-0.5 Smooth downward granular bed flow with nofluidization. 0.5-0.8 Smooth downward granular flow. Bed beginning toexpand against screen with slight fluidization on top. 0.8-1.5 Smoothdownward granular flow. Full expansion against the screen with nofluidization present. >1.5 Top half of granular bed in downcomer isstationary and fully expanded against screen while bottom half becomesfluidized.

By increasing gas throughput, the overall size of the filter isdecreased resulting in reduced costs associated with manufacturing theunit. At the same time, the low pressure drop decreases the operatingcosts by reducing the energy required by a blower to move gas throughthe filter. Furthermore, even distribution of gas at the interfacebetween entering gas and the granular bed assures that granules of bedmaterial and dust collected on the granules is not disturbed, whichwould adversely impact filtration efficiency.

The gas throughput with and without the screen installed in thedisengagement section of the filter was measured. Without the screen,the maximum gas flow occurred when the moving bed began to fluidize.With the screen installed, the maximum gas flow occurred when gas flowin the lower region of the bed became turbulent and disrupted the smoothdownward flow of granules. As indicated, the screen increased gasthroughput by 67% compared to the filter operated without the screen.Observations on the behavior of the granular bed in the presence andabsence of the screen are recorded in Tables 2 and 3.

Without the screen, granules at the surface of the bed in thedisengagement section become agitated with increasing fluidizationvelocity and eventually blowout of the filter. It is estimated that themaximum operating velocity to be 182 ft/min with a screen. When a screenwas installed in the disengagement section, the granules expandedagainst the screen but were not able to fluidize. The maximum operatingvelocity was estimated to be 303 ft/min.

TABLE 2 Granular Bed Effects in Gas Disengagement Section Without ScreenSuperficial Gas Velocity (ft/min) Granular Bed Effects 0-61 Smoothdownward granular bed flow with no fluidization. 91-121 Smooth downwardgranular bed flow. Beginning to expand to top of gas disengagement flow.152-182  Smooth downward granular bed flow. Full expansion of the bedwith the uppermost regions becoming fully fluidized. >182 Top half ofbed fully fluidized; granular material entrained and blown out of thefilter.

TABLE 3 Granular Bed Effects in Gas Disengagement Section with ScreenSuperficial Gas Velocity (ft/min) Granular Bed Effects  0-91 Smoothdownward granular bed flow with no fluidization. 121-152 Smooth downwardgranular bed flow. Bed beginning to expand against screen with slightfluidization on top. 182-303 Smooth downward granular bed flow. Fullexpansion against the screen with no fluidization present. >303 Top halfof granular bed is stationary and fully expanded against screen withbottom half becoming fluidized.

The two types of inlets investigated were a conventional gas inletentering perpendicularly to the body of the filter and a gas inletentering tangentially to the body of the filter with flow straighteningfins. Both configurations employed screens in the disengagementsections. Pressure loss was significantly less for the tangential inletthan for the perpendicular inlet. At the maximum operable superficialgas velocity of 303 ft/min the pressure loss for the tangential inletwas 44% less than for the perpendicular inlet.

The momentum of the gas was better conserved using the tangential gasinlet. When the gas entered through the tangential gas inlet, themomentum of the horizontally flowing gas was efficiently converted tocyclonic flow in the body of the filter. On the other hand, when the gaswas injected perpendicularly into the filter, the gas lost momentum asthe flow is rearranged.

As previously indicated, in tests with the tangential inlet,flow-straightening fins were employed just above the gas engagementsection to prevent scouring of the interfacial region of the bed, assubsequently described. Pressure loss was significantly less for thetangential inlet than for the perpendicular inlet. At the maximumoperable superficial gas velocity of 1.5 m/s the pressure loss for thetangential inlet was 44% less than for the perpendicular inlet.

The behavior of granules at the surface of the moving bed where gasentered was observed as a function of superficial velocity. Observationsfor-the perpendicular and tangential gas inlets are recorded in Tables 4and 5, respectively.

TABLE 4 Gas-Solid Contacting Region Effects Using Perpendicular GasInlet and Screen Superficial Gas Velocity (ft/min) Gas-Solid ContactingRegion Effects  0-182 Interface is smooth with no scouring present.212-303 Interface becomes scoured on side opposite of gas inletindicating uneven gas distribution.

TABLE 5 Gas-Solid Contacting Region Effects using Tangential Gas Inlet,Screen, and Fins Superficial Gas Velocity (ft/min) Gas-Solid ContactingRegion Effects 0-303 Interface is smooth with no scouring present. >303Gas is evenly distributed as granular interface becomes slightly scouredcompletely around gas disengagement section.

For the perpendicular inlet, the gas flow appeared to be uniformlydistributed over the granular bed interface up to superficial velocityof 182 ft/min. However, above this velocity, the interface of the bed onthe side opposite of the inlet was strongly scoured, with granulesviolently tossed about. On the other hand, the tangential inlet showeduniform gas distribution at velocities as high as 303 ft/min.

High momentum gas entering the perpendicular inlet was not able tosmoothly negotiate the downward turn and becomes concentrated at a pointon the surface of the bed immediately opposite the inlet, the scouringeffect showed how the gas was unevenly distributed over the gas-solidcontact region. On the other hand, the tangential inlet combined withflow straightening fins, efficiently turns the flow and distributes itover the granular bed interface.

Although the tangential inlet greatly reduces pressure drop in thefilter, the cyclonic flow scours the surface of the granular bed,disrupting the formation of dust cake deposited by entering gas. Thefins which were installed in the annular space formed below the inletconduit did straighten gas streamlines flowing downward toward theengagement section of the granular bed. Qualitative observations weremade of the bed surface as a function of superficial gas velocity forperpendicular and tangential gas inlets and recorded in Tables C and D,respectively.

TABLE C Behavior of granules at bed interface with no fins in gasengagement region Superficial gas Velocity (m/s) Gas-solid contactingregion observations   0-0.9 Gas engagement interface is smooth with noscouring. 0.9-1.5 Interface becomes scoured on side opposite of gasinlet.

TABLE D Behavior of granules at bed interface with fins in gasengagement region Superficial gas Velocity (m/d) Gas-solid contactingregion observations 0-1.5 Gas engagement interface is smooth with noscouring. >1.5 Gas is evenly distributed with little scouring.

The counterflow moving bed granular filter design handles a high gasthroughput and produces a low-pressure drop while evenly distributingthe gas over the gas-solid contacting region. These effects are achievedby using three main design features: a tangential gas inlet, a flowstraightening section, and a screened gas disengagement section. Thecold flow tests indicate that these design features can improve theperformance of moving bed granular filters.

DESCRIPTION OF ALTERNATE EMBODIMENT

FIG. 4 shows an alternate form of the invention which includesessentially the same structure contemplated by FIGS. 1-3, except that adiamond shaped insert 64 supported generally on fins 34 in theconfiguration of a plumb bob has an inverted conical shaped top 66 and aconical shaped bottom 68 with side walls 70. The side walls 70 arespaced from the sidewalls 36 of bottom 18 to provide a conical shapedmaterial passageway 72. The shape of the insert 64 creating thepassageway 72 beneficially changes the media flow pattern, whichenhances the flow and performance of the filter material 48. It alsoserves to reduce the change of the media in the filter which reducesstart up time. More specifically, the presence of the diamond-shapedinsert 64 serves to encourage mass flow of the filter media, therebydirecting the filter media to the gas/media interfacial region 50.Exchange of clean filter media for dirty filter media in the interfacialregion 50 is critical for high efficiency filtration.

Among the advantages of the embodiments of the present invention are thefollowing:

1. The disengagement section 22 employs a screen 32 to prevent the freeexpansion of the granular bed 48A. This constraint prevents the bed 48Afrom fluidizing, which would otherwise limit the maximum gas flow ratethrough the filter.

2. With use of flow-straightening fins 34, the tangential gas inlet 54provides a low-pressure drop as the gas enters a moving bed granularfilter. This reduces pumping costs and provides a more energy efficientfilter.

3. With use of flow-straightening fins 34 in combination with thetangential gas inlet 54, the gas is evenly distributed over thegas-solid contacting region. This maximizes gas-granule contact time andprovides even utilization of the granular bed.

4. The use of the diamond shaped insert 64 serves to beneficially changethe media flow pattern, which enhances the flow of the filter material48.

It is therefore seen that this invention will accomplish at least all ofits stated objectives.

1. A method for filtering gas with a moving granular filter bed,comprising, providing a cylindrical filter compartment having a top,bottom, and cylindrical side walls, providing an upward compartmentportion below the top of the filter compartment, and having a bottomportion with an opening therein, providing a conduit extending throughthe top of the filter compartment and through the opening in the bottompartition of the upper compartment portion, providing that the openingin the bottom partition of the upper compartment is sufficiently largeto create a space around the hollow conduit, providing a screen mesh forcovering the space around the hollow conduit, providing a gas engagementportion in the cylindrical filter compartment which has a diametergreater than the space around the hollow conduit to receive a quantityof filter material moving through the hollow conduit, passing a quantityof particulate filter material through the hollow conduit and into thegas engagement portion of the cylindrical filter compartment,restraining the vertical flow of particulate filter material downwardlythrough the gas engagement portion sufficiently to create a quantity offilter material sufficient to engage the entire area of the screen mesh,introducing a jet of horizontal gas tangentially into the gas engagementportion to direct gas in a cyclonic direction around the moving granularfilter material in the gas engagement portion, and providing a gas exitport in the upper compartment portion to permit the exit of gastherefrom which has migrated through the particulate filter material inthe gas engagement portion, thence through the screen mesh, and thenceinto the upper compartment.
 2. The method of claim 1 wherein theparticulate filter material is comprised of particles which arespherical in shape.
 3. The method of claim 2 wherein the particulatematerial is comprised of soda-lime glass beads.
 4. The method of claim 3wherein the soda-lime glass beads are approximately 4-mm in diameter. 5.The method of claim 1 wherein the particulate material is comprised ofsoda-lime glass beads.
 6. The method of claim 1 wherein the cyclonicpath of the gas through the gas engagement section is diverted to adownwardly vertical flow towards the bottom of the filter compartment.7. The method of claim 1 wherein a baffle element having a diamond shapewith tapered side walls in a lower portion thereof is suspended in thelower portion of the filter compartment in spaced relation to taperedexterior walls of the filter compartment to provide a conically shapedpassageway of the particulate material downwardly through the filtercompartment.
 8. The method of claim 1 wherein the vertical hollow inletconduit is connected to a source of filter material sufficiently to havea quantity of moving filter material filling the hollow conduit as thematerial moves therethrough.
 9. The method of claim 1 wherein the filtermaterial in the bottom of the filter compartment is movably removed fromthe filter compartment without allowing any of the gas in the filtercompartment to also exit the filter compartment.
 10. A filter forbiomass gasification, comprising, a cylindrical filter compartmenthaving a top, bottom and cylindrical side walls, an upper compartmentportion below the top of the filter compartment, and having a bottompartition with an opening therein, a vertical hollow conduit extendingthrough the top of the filter compartment and the opening in the bottompartition of the upper compartment portion, the opening in the bottompartition of the upper compartment being sufficiently large to create aspace around the hollow conduit, a screen mesh covering the space aroundthe hollow conduit, a gas engagement portion in the cylindrical filtercompartment having a diameter greater than the space around the hollowconduit to receive a quantity of filter material moving through thehollow conduit, and being sufficiently large to contain at least aconical-shaped pile of filter material flowing out of the hollow conduitsufficient to engage the entire area of the screen mesh, a substantiallyhorizontal gas inlet port tangentially positioned on the gas engagementportion to direct gas into the interior of the gas engagement portion todirect gas in a cyclonic direction around an accumulation of movinggranular filter material moving through the gas engagement portion, anda gas exit port in the upper compartment portion to permit the exit ofgas therefrom which has entered the gas engagement portion, thenceengaged and passed through the accumulation of moving filter material inthe gas engagement portion, and thence through the screen mesh and intothe upper compartment.
 11. The filter of claim 10 wherein a plurality ofvertically positioned radially extending fins are mounted in the gasengaging portion below the gas inlet port.
 12. The filter of claim 10wherein a baffle element having the shape of an inverted cone issuspended in the lower portion of the filter compartment in spacedrelation to tapered exterior walls extending downwardly from thecylindrical walls of the filter compartment, and being located above inthe bottom of the filter compartment.
 13. The filter of claim 12 whereina plurality of vertically positioned radially extending fins are mountedin the gas engaging portion below the gas inlet port.
 14. The filter ofclaim 10 wherein the vertical hollow conduit is connected to a source offilter material sufficient to have a quantity of moving filter materialfilling the hollow conduit as it moves therethrough.
 15. The filter ofclaim 10 wherein a sealed disposal means is located in the bottom of thefilter compartment to receive filter material that has passed throughthe filter compartment.
 16. The filter of claim 10 wherein means areprovided at the bottom of the filter compartment for allowing filtermaterial to exit therefrom without allowing gas within the filtermaterial to exit the filter compartment.